Considerable interest exists in long-term treatment effects in cancer survivors that can have a significant impact on quality-of-life (QOL) outcomes. Cognitive impairment is one of the most common QOL complaints among breast cancer survivors; as many as 70% report memory loss and difficulty concentrating, however, objective tests of cognitive function typically show only 15% - 25% of survivors are impaired based on normative criteria. This discrepancy between the high prevalence of subjective complaints and more modest deficits observed in objective tests may be because standard neuropsychological assessments in controlled laboratory or clinic conditions do not map on to the daily activities in which survivors report problems. Second, cognitive impairments may be subtle and although noticeable to a survivor reflecting on her pre-treatment performance, these within-person changes may not be detectible as differences between survivors. Finally, cognitive impairment among breast cancer survivors may be related to other common QOL outcomes (e.g., stress, depression, fatigue) which may differ between people and fluctuate for a given survivor across time. That is, a survivor may have good days and bad days in terms of her daily cognitive functioning, and these fluctuations may be predicted by whether she is feeling fatigued, depressed, or stressed on that day. To address these issues, data will be collected from breast cancer survivors who were treated with chemotherapy. Cognitive functioning will be assessed in these individuals using self-report questionnaires and neuropsychological instruments as well as with daily diary reports of memory failures, and cognitive tasks administered as `brain games' on smartphones across a 14-day period. Innovations in mobile data collection allow for real-time capture of objective cognitive performance and subjective cognitive complaints. This R03 addresses these specific aims: (1) determine if cognitive performance assessed in laboratory settings is an accurate representation of the kinds of daily cognitive challenges that cancer survivors experience, and (2) determine if survivors' daily performance can be predicted by how fatigued, depressed, or stressed they feel that day. The approach is innovative, in the applicant's opinion, because it leverages novel approach of assessing cognitive performance in the field in order to answer important questions in survivorship research: which survivors experience cognitive deficits and when are these deficits most likely to occur. This study is significant, as the resolution of these issues will direct the development of interventions to reduce the frequency and impact of cognitive deficits among breast cancer survivors.